0028487: Visualization, TKOpenGl - add option for rendering with lower resolution

0028487: Visualization, TKOpenGl - add option for rendering with lower resolution

Graphic3d_RenderingParams::RenderResolutionScale - added new option
defining scale factor for allocating off-screen rendering buffers
relative to native resolution of window buffer.

Scale factor can be below 1.0 (lower resolution) or higher (as analog of super sampling),
but can not be combined with MSAA settings.

Draw Harness command vrenderparams has been extended with option -rendScale
managing introduced option Graphic3d_RenderingParams::RenderResolutionScale.

vcaps has been extended with option -useWindowBuffer for managing
OpenGl_Caps::useSystemBuffer option.

vrepaint has been extended with option -immediate
for testing immediate layer redraw

OpenGl_View::blitBuffers() - eliminate compiler warning on Android